Combustion Synthesis of Lanthanum Substituted LiNiO₂ Using Hexamine as a Fuel

Abstract

Lithium nickelate and its lanthanum substituted compound have been successfully prepared by combustion synthesis process using LiNO₃, Ni(NO₃)₂.6H₂O and La(NO₃)₃.6H₂O. Hexamine is used as fuel. The physicochemical properties of the powders were investigated by thermal analysis (TGA/DTA). The crystalline powders were characterized for their phase identification using x-ray diffraction analysis (XRD). FT-IR spectroscopy was used to study the local structure of the oxide environment. The morphological features of the powders were characterized by scanning electron microscopy (SEM). DTA analysis reveals the evolution of an exothermic peak at 465 ^oC indicating the rapid decomposition of the hexamine and dissociation of nitrate salts, forming the final compound lithium nickealte. The XRD pattern reveals the rhombohedral structure of LiNiO₂ with trigonal symmetry comprising of two interpenetrating close packed FCC sub-lattices. The lattice constant values ̒a̓ and ̒c̓ are in good agreement with the reported data. In the FT-IR spectra, vibrational bands are identified in the range of 400-800 cm^-1 representing the NiO₂ layer. LiNiO₂ exhibits a very fine crystalline structure with an irregular morphology. The La substituted LiNiO₂ powder has shown a smooth-edged polyhedral structure with an average particle size of 5-10 μm.